Reserver policy parameter of disks!

Dears, We have here a per-implemented environment Oracle RAC 10g under AIX 5.3 with GPFS with DS4800 SAN, As I know from my personal experience we have to change the reserve_policy parameter on voting disk only from single path to (no_reserve), now I have 2 questions:

1. Should we have to change all shared disks from (reserve_policy _single_path_) to (reserve_policy_no_reserve_)? or is it enough to apply this only on voting disks?

2. If so, could we change this reserve_policy parameter online from single_path to no_reserve?

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1. I believe to turn off device locking, the reserve plicy for all the shared disks should be set to no_reserve

2. You cannot, it means the change will not take effect online, you need to set this characteristic before you plan to use the disk, now there are 2 options,
a) one is to unmount the FS, varyoff the VG, put the disks in defined state (rmdev -l <hdisk##>), then change the reserve policy, the command is
chdev -l hdisk## -a reserve_policy=no_reserve

b)This option is to make the changes first and then reboot the machine when time permits to take the effect of the no_reserve attribute

It is a must if you expect the disks are shared between hosts and can be accessed by the initiators either on the same host or on different. By default the SCSI reservation methodology is applied to the device depending upon the MPIO in use. In your case you are using DS48K with AIX native MPIO which sets the reserve_policy to single path, In order to use multiple paths with native MPIO the reserve_policy must be set to no_reserve (Other initiator can access the device on the same host), and SDDPCM by default sets the reserve_policy attribute to no_reserve. Not to confuse you but it completely depends on your requirement.

But if I change reserve policy of a disk, does that change any physical parameter on the disk or it simply does a change in odm. Why am I asking this is because whenever I add disks to vio client my mapping from vio server, I had to change the reserve policy to "no" in both vios.if the reserve policy changes affects the physical disk then change only in one vio is required.

Reserve policy applies for the device.So for mpio the same lun from the san
is mapped to 2 vio servers(for 2 paths), in this case you may need to set your
reserve policy to no and after doing that only you can map the luns in both
vio.If there is reservation set to single path then you can only map to one
vio and not to the other.

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